Environmental health risks and benefits of the use of mosquito coils as malaria prevention and control strategy.

BACKGROUND: Malaria is an infectious disease that causes many deaths in sub-Saharan Africa. In resource-poor malaria endemic communities, mosquito coils are commonly applied in households to repel the vector mosquito that transmits malaria parasites. In applying these coils, users have mainly been interested in the environmental health benefits potentially derived from repelling the mosquito, while oblivious of the environmental health risks that may be associated with exposure to emissions from the use of mosquito coil. This study evaluated the effectiveness of the mosquito coil, ascertained and/or estimated the toxic emissions that may emanate from the coil, and determined its overall appropriateness by conducting a risk-benefit analysis of the use of this strategy in malaria prevention at household levels. METHODS: The repellent ability of mosquito coils was tested by conducting a mosquito knockdown/mortality test in experimental chambers synonymous of local room spaces and conditions. The gaseous and particulate emissions from the mosquito coil were also analysed. Additional scenarios were generated with the Monte Carlo technique and a risk-benefit analysis was conducted applying @Risk software. RESULTS: Mosquito mortality arising from the application of various mosquito coils averagely ranged between 24 and 64%, which might not provide adequate repellency effect. Emissions from the mosquito coil were also found to contain CO, VOCs, SO2, NO2, PM2.5 and PM10. The Hazard Index of the respective pollutants characterized over a lifetime exposure scenario was low (< 1 for each pollutant), which suggests that the concentrations of the specific chemicals and particulate matter emitted from the mosquito coil may not constitute adverse environmental health risk. CONCLUSION: Although the risk of morbidity from the use of the mosquito coil was low, the coil yielded limited protection as a mosquito avoidance method. It may, therefore, have a reduced benefit in controlling malaria and should be applied sparingly in a highly regulated manner only when traditionally proven effective vector control strategies are not available or too expensive for resource-poor malaria endemic regions.

Synthesis and characterization of nitrile functionalized silver(I)-N-heterocyclic carbene complexes: DNA binding, cleavage studies, antibacterial properties and mosquitocidal activity against the dengue vector, Aedes albopictus.

A series of four benzimidazolium based nitrile-functionalized mononuclear-Ag(I)-N-heterocyclic carbene and binuclear-Ag(I)-N-heterocyclic carbene (Ag(I)-NHC) hexafluorophosphate complexes (5b-8b) were synthesized by reacting the corresponding hexafluorophosphate salts (1b-4b) with Ag2O in acetonitrile, respectively. These compounds were characterized by 1H NMR, 13C NMR, IR, UV-visible spectroscopic techniques, elemental analyses and molar conductivity. Additionally, 8b was structurally characterized by single crystal X-ray diffraction technique. Preliminary in vitro antibacterial evaluation was conducted for all the compounds against two standard bacteria; gram-positive (Staphylococcus aureus) and gram-negative (Escherichia coli) bacterial strains. Most of the Ag(I)-NHC complexes (5b-8b) showed moderate to good antibacterial activity with MIC values in the range of 12.5-100 µg/mL. Especially, compound 8b exhibited promising anti-Staphylococcus aureus activity with a low MIC value (12.5 µg/mL). However, all the hexafluorophosphate salts (1b-4b) were inactive against the bacteria strains. The preliminary interactive investigation revealed that the most active compound, 8b, could effectively intercalate into DNA to form 8b-DNA complex which shows a better binding ability for DNA (Kb = 3.627 × 106) than the complexes 5b-7b (2.177 × 106, 8.672 × 105 and 6.665 × 105, respectively). Nuclease activity of the complexes on plasmid DNA and Aedes albopictus genomic DNA was time-dependent, although minimal. The complexes were larvicidal to the mosquito, with 5b, 6b and 8b being highly active. Developmental progression from the larval to the adult stage was affected by the complexes, progressively being toxic to the insect's development with increasing concentration. These indicate the potential use of these complexes as control agents against bacteria and the dengue mosquito Ae. albopictus.

To coil or not to coil: application practices, perception and efficacy of mosquito coils in a malaria-endemic community in Ghana.

Although evidence of mosquito coils' impact on disease epidemiology is limited, they are popularized as mosquito-borne disease prevention devices. Their usage affects the environment, human and mosquito health. This study investigated the perception, usage pattern and efficacy of coils in a predominantly poor malaria-endemic Ghanaian peri-urban area. Information on protection methods, perception and usage pattern was garnered using questionnaires. The efficacy of commonly used coils in the area was then assessed on the malaria vector, Anopheles gambiae, in a glass chamber. Sole or co-application of mosquito control methods and risky usage practices were reported. Coils were deemed harmful to humans and mosquitoes, and their perceived effectiveness varied, with several factors influencing their purchase. High d-allethrin concentration coils induced quicker mosquito knockdown; however, mortality was less than 85%. The coil usage pattern compromises users' health and can enhance mosquito tolerance to d-allethrin. The coils were ineffective against the vector, outlining a dichotomy between the users' perception of efficacy and the observed efficacy. Hence, the usage of other safer and more effective vector control methods should be encouraged to protect households.

Dinuclear silver(I)-N-heterocyclic carbene complexes: Synthesis, characterization and larvicidal activity of bis-imidazolium dinuclear silver(I)-N-heterocyclic carbene complexes.

New synthesized bis-imidazolium salts that are linked by xylyl derivatives moiety, 1-4 was reacted with Ag2O to facilitate the formation of dinuclear Ag(I)-N-heterocyclic carbene (NHC) complexes, 5-8, respectively. All the synthesized ligand salts and complexes were characterized by 1H and 13C NMR, FTIR spectroscopy and elemental analysis. Molecular structures of compounds 3, 5, and 7 were elucidated by single crystal X-ray diffraction analyses. Larvicidal studies against the Aedes aegypti and Culex quinquefasciatus were carried out on all synthesized compounds following the World Health Organization standard larval susceptibility test. All the imidazolium salts were found inactive while the activity of the dinuclear Ag(I)-NHC complexes on mosquito larvae are varies with the nature of the ligands. Complex 7 has high activity on Ae. aegypti and Cx. quinquefasciatus, emphasising its potential as a larvicidal compound.

Molecular cloning, sequence analysis and developmental stage expression of a putative septin gene fragment from Aedes albopictus (Diptera: Culicidae).

Septins belong to GTPases that are involved in vital cellular activities, including cytokinesis. Although present in many organisms, they are yet to be isolated from Aedes albopictus. This study reports for the first time on a serendipitous isolation of a partial septin sequence from Ae. albopictus and its developmental expression profile. The Ae. albopictus partial septin sequence contains 591 nucleotides encoding 197 amino acids. It shares homology with several insect septin genes and has a close phylogenetic relationship with Aedes aegypti and Culex quinquefasciatus septins. The Ae. albopictus septin fragment was differentially expressed in the mosquito's developmental stages, with an increased expression in the adults.

Identification and analysis of a processed cytochrome P450 pseudogene of the disease vector Aedes aegypti.

OBJECTIVE: To clone cytochrome P450 from Aedes aegypti (Ae. aegypti) and determine the characteristics using bioinformatics tools. METHODS: Cytochrome P450 of Ae. aegypti was amplified using polymerase chain reaction, cloned and sequenced. Evolutionary relationship of the sequence was inferred and bioinformatics tools were used to predict subcellular localisation, signal peptide, transmembrane helix, phosphorylation, O-glycosylation, secondary and tertiary structures of the deduced protein. RESULTS: Polymerase chain reaction rather amplified a cytochrome P450 pseudogene which was named CYP4H44P (GenBank accession number KF779932). The pseudogene has 1537 nucleotides and an open reading frame of 335 amino acids containing cytochrome P450 motifs except the WxxxR motif. It is highly homologous to CYP4H28 and CYP4H28v2. Phylogenetic analysis and evolutionary divergence showed strong clustering with CYP4H28 alleles and least divergence from the alleles respectively. The deduced protein was predicted to be found in the cytoplasm and likely to be phosphorylated but devoid of signal peptide, transmembrane helix and O-glycosylated sites. The secondary and tertiary structures were also generated. CONCLUSIONS: A cytochrome P450 pseudogene, CYP4H44P was cloned from Ae. aegypti. The pseudogene is homologous with CYP4H28 alleles and seems to have recently diverged from this group. Isolating this pseudogene is an important step for evaluating its biological role in the mosquito and for the evolutionary analysis of Ae. aegypti CYPs.

Insecticidal activity and expression of cytochrome P450 family 4 genes in Aedes albopictus after exposure to pyrethroid mosquito coils.

Mosquito coils are insecticides commonly used for protection against mosquitoes due to their toxic effects on mosquito populations. These effects on mosquitoes could induce the expression of metabolic enzymes in exposed populations as a counteractive measure. Cytochrome P450 family 4 (CYP4) are metabolic enzymes associated with a wide range of biological activities including insecticide resistance. In this study, the efficacies of three commercial mosquito coils with different pyrethroid active ingredients were assessed and their potential to induce the expression of CYP4 genes in Aedes albopictus analyzed by real-time quantitative PCR. Coils containing 0.3 % D-allethrin and 0.005 % metofluthrin exacted profound toxic effects on Ae. albopictus, inducing high mortalities (≥90 %) compared to the 0.2 % D-allethrin reference coil. CYP4H42 and CYP4H43 expressions were significantly higher in 0.3 % D-allethrin treated mosquitoes compared to the other treated populations. Short-term (KT50) exposure to mosquito coils induced significantly higher expression of both genes in 0.005 % metofluthrin exposed mosquitoes. These results suggest the evaluated products provided better protection than the reference coil; however, they also induced the expression of metabolic genes which could impact negatively on personal protection against mosquito.

Pyrethroid resistance in Anopheles gambiae, in Bomi County, Liberia, compromises malaria vector control.

BACKGROUND: Long Lasting Insecticidal Nets (LLIN) and Indoor Residual Spraying (IRS) have both proven to be effective malaria vector control strategies in Africa and the new technology of insecticide treated durable wall lining (DL) is being evaluated. Sustaining these interventions at high coverage levels is logistically challenging and, furthermore, the increase in insecticide resistance in African malaria vectors may reduce the efficacy of these chemical based interventions. Monitoring of vector populations and evaluation of the efficacy of insecticide based control approaches should be integral components of malaria control programmes. This study reports on entomological survey conducted in 2011 in Bomi County, Liberia. METHODS: Anopheles gambiae larvae were collected from four sites in Bomi, Liberia, and reared in a field insectary. Two to five days old female adult An gambiae s.l. were tested using WHO tube (n=2027) and cone (n=580) bioassays in houses treated with DL or IRS. A sample of mosquitoes (n=169) were identified to species/molecular form and screened for the presence of knock down resistance (kdr) alleles associated with pyrethroid resistance. RESULTS: Anopheles gambiae s.l tested were resistant to deltamethrin but fully susceptible to bendiocarb and fenithrothion. The corrected mortality of local mosquitoes exposed to houses treated with deltamethrin either via IRS or DL was 12% and 59% respectively, suggesting that resistance may affect the efficacy of these interventions. The presence of pyrethroid resistance was associated with a high frequency of the 1014F kdr allele (90.5%) although this mutation alone cannot explain the resistance levels observed. CONCLUSION: High prevalence of resistance to deltamethrin in Bomi County may reduce the efficacy of malaria strategies relying on this class of insecticide. The findings highlight the urgent need to expand and sustain monitoring of insecticide resistance in Liberian malaria vectors, evaluate the effectiveness of existing interventions and develop appropriate resistance management strategies.